In conventional magnetic tumbler cylinders, the magnetic key used to operate the lock is not formed with notches such as a pin cylinder, and therefore, the key can be inserted and disengaged from the key hole very smoothly at any angular location. As a result the key may be disengaged during rotation of the cylinder resulting in a possible incomplete operation. Particularly when the key is disengaged from a position other than the normal position during the locking operation, the tumbler is not fully engaged within the tumbler groove so the cylinder remains free to rotate and thus the lock mechanism may be unlocked by means of any key or other tool without need for the correct key. In order to prevent the disadvantages noted above, there is proposed a method (Japanese Design Registration No. 378,792 and Japanese Utility Model Publication No. 25,586/71) in which recess portions are provided in the key and inner cylinder, and ball or pin is placed in which engagement with said recess portions or a method in which a convex portion is provided in a part of a key and said convex portion engages a part of an inner cylinder so as to avoid insertion and removal of a key from key hole at a position other than the normal position. However, in case of these methods, since the ball or pin and the convex portion of the key are interengaged the function of preventing removal of the key fails if the precision thereof is poor or if use thereof is made for a long period of time even though the precision is good with the result that a wear occurs, and as a consequence, phenomenon of removal of a key from key hole at an undesirable position occurs, thus suffering from occurrence of such a trouble as noted above.
In order to eliminate those disadvantages noted above with respect to prior arts, the present invention provides an arrangement wherein a plurality of disengagement preventive pins are provided within a conventional magnetic tumbler cylinder, said pins each being divided into an upper pin segment and a lower pin segment and a correct key therefore is provided with a plurality of the corresponding key magnets and recesses in engagement with the lower pin segment so that when a correct key is inserted into a key hole, the magnetic tumbler and a border surface between the upper pin segment and the lower pin segment are respectively aligned with a shear line permitting rotation of the cylinder.
The advantages of the present invention may be summarized as follows:
(1) Since the disengagement preventive pins provided are plural in number instead of a single as in prior arts, the normal position at which a correct key is disengaged is far more accurate as compared to prior arts. In addition, even after use for many years, the precision can be maintained sufficiently.
(2) The ancillary effect of the present invention is that in a state where a key is pulled out of the cylinder, that is, in a locked state, the upper pin segment 6 interrupts the shear line, and therefore, even if an attempt is made to forcibly rotate the inner cylinder 2 falsely by means of a screw driver or the like, a plurality of upper pin segments 6 bear a part in restricting such forcible rotation, thereby greatly increasing the resistance to forcible rotation thereof as compared to the conventional cylinder merely comprising a magnetic tumbler.
(3) Further, in an attempt of so-called picking, in the case of the conventional magnetic tumbler cylinder, arrangement of magnetic poles can read externally by some means resulting in a possible reproduction of a key. However, the present invention provides a further ancillary effect that the magnetic tumbler may be moved in a manner as described and at the same time, a border surface between the lower pin segment 5 and the upper pin segment 6 of a plurality of disengagement preventive pins has to be aligned one by one with the shear line. False unlocking (picking) in which the complicated operations for the individual alignment of both groups of magnetic tumblers and group of disengagement preventive pins within a narrow limited space which is a key hole are simultaneously executed is extremely difficult, and thus the safety of the lock device increased greatly as compared to the conventional magnetic tumbler cylinder.